1. Technical Field
The present invention relates to a semiconductor substrate, to a semiconductor device, to a method of manufacturing a semiconductor substrate, and to a method of manufacturing a semiconductor device. In particular, the invention is preferably applied to a method in which an SOI structure and a bulk structure exist together on the same substrate.
2. Related Art
Field effect transistors formed on an SOI substrate have been of main interest in terms of convenience of element separation, latch-up free property, small source/drain junction capacitance, and so on. In particular, since a complete depletion-type SOI transistor has features, such as low power consumption, high speed operation, and low-voltage driving, research for operating an SOI transistor in the total depletion mode has been actively carried out. Here, as the SOI substrate, a SIMOX (separation by implanted oxygen) substrate or a bonded substrate is used, for example.
On the other hand, it is difficult to form the field effect transistor, which has a large power for current driving and requires a high withstanding voltage, on the SOI substrate in which the thickness of a silicon layer is limited. Therefore, it is required that the field effect transistor be formed on the bulk substrate.
For example, Japanese Unexamined Patent Application Publication No. 2003-203967 discloses a method in which a silicon layer and a BOX layer disposed on a part of an SOI substrate are selectively removed and an epitaxial silicon layer is formed on the part thereof to thereby form a non-SOI region on the SOI substrate, so that SOI transistors and transistors capable of withstanding high voltages can exist together on the same substrate.
However, in order to manufacture the SIMOX substrate, high-concentration oxygen ions are needed to be implanted into a silicon wafer. In addition, in order to manufacture the bonded substrate, it is required to polish the surface of the silicon wafer after two wafers are bonded to each other. For this reason, in the method in which the non-SOI region is provided on the SOI substrate, manufacturing costs increase as compared to a method in which the field effect transistors are formed in a bulk semiconductor.